This section investigates the functional properties of excitatory amino acid receptors in the vertebrate CNS, utilizing electrophysiological and molecular biological techniques. Concentration jump techniques are used to apply glutamate receptor selective agonists and antagonists to cells and membrane patches under voltage clamp. Preparations in use include recombinant receptors expressed in transfected mammalian cells and Xenopus oocytes, and native receptors generated in primary cultures of hippocampal neurons and glial cells. Analysis of the molecular basis of allosteric regulation of AMPA receptors is being investigated by generation of mutants in which conserved amino acids which differ between the alternative flip/flop exons are tested for sensitivity to potentiation by cyclothiazide and noncompetitive inhibition by 2,3- benzodiazepines. In experiments on hippocampal neurons multiple rate constants for recovery from potentiation by cyclothiazide suggest the existence of heteromeric receptors with different ratios of subunits in their flip and flop splice versions. Inward rectification of glutamate receptors unedited in the second membrane domain was shown to result from ion channel block by micromolar concentrations of cytoplasmic polyamines.